Modern firearms, in particular, military assault rifles, can be deployed for a number of combat missions such as sniper weapons and in close combat. They are commonly used for nighttime combat. All of these applications can require fitting a variety of telescopic sights, infrared sights, tactical lights, laser sighting modules, grenade launchers, bipods, grips and other accessories to the firearm. For mounting purposes, standardized mounting platforms have been developed, such as the Picatinny rail platform (MIL-STD-1913 or STANAG 2324). The Picatinny rail is a cross-section shaped roughly like a wide T with the top of the T corresponding to the top of the rail. The rail has a number of evenly spaced transverse slots in the top spanning the width of the T-shaped cross-section.
Such rails are often placed directly on the weapon's receiver, in the position normally occupied by the rear sights. The rail may also extend over the rifle handguard associated with the rifle barrel. In addition to top mounting rails, firearms may now include rails fastened to guns in various locations. In some cases, grips are surrounded with top, bottom and side rails. Mounting rails are also appearing on shotguns and pistols.
While the mounting rails have obvious utilitarian benefits, they are not without some shortcomings. Most notably, they can be uncomfortable when grasped by a user's hands, they can snag on clothing, barbed wire, and other objects, they add weight to a weapon system, and under certain field conditions they may become clogged with dirt and other debris that make it difficult to install one of the many accessories receivable on the rails.
Other systems have detachable rails that allow the user to install rails only where they are needed, and only of the length needed. While this decreases weight (and the discomfort and other disadvantages) of having needless rails where the hand is to grip, it suffers from other disadvantages. First, such systems may be difficult or complex to install. Second, they may require custom modification of parts, such as drilling and tapping holes where needed. Third, the attachment locations may be in limited locations due to the need to relocate fasteners such as threaded inserts (or may increase cost and weight by using an excessive number of fasteners).
A further significant disadvantage of systems having modular rails that may be mounted in various locations on the forearm or handguard of a rifle stock is the susceptibility to loosening. If the mount for a rifle scope becomes loose, this can cause significant aiming errors.
One solution to the disadvantages of Picatinny rail systems is the KEYMOD system introduced by VLTOR Weapon Systems. The KEYMOD system consists of two parts: the KEYMOD slot; and the KEYMOD nut. The slot is distinctive with a larger diameter through-hole combined with a narrow slot. The slot is chamfered on the backside while the through-hole is sized for clearance of a quick-detach sling swivel (approximately ⅜″ diameter).
However, the KEYMOD specifications also suffer from several disadvantages including more complex manufacturing. The KEYMOD specification is also harder to implement in polymeric materials since it typically requires complex secondary machining operations rather than standard molding processes to form the keyhole apertures. Therefore, there is a need in the art for a firearm accessory mounting interface that adds minimal or no weight to a weapon system, is unlikely to snag, is unlikely to clog with mud and debris, and is comfortable to hold.